Tokukouhei 5-17401, which is was published by the Japanese Patent Office in 1993, discloses a signal processor which outputs a current according to an input voltage from a joystick input device in order to control a device that is controlled by a proportional solenoid valve or the like. This is done by varying the valve opening of the proportional solenoid valve according to an amount by which a joystick is inclined from a neutral position, and thereby controls the motion of a hydraulic actuator.
FIG. 6 is a characteristic diagram showing the relation of a time t from when the joystick is operated, and a displacement amount S of the hydraulic actuator which is hydraulically driven via the proportional solenoid valve. In a conventional device, as shown by the single dotted line, a time a until the actuator begins to move is long, and response is poor. This may be due to a delay with which the current output to the proportional solenoid valve appears due to the inductance produced in a coil, or to an overlap part in which the flow of working oil in the proportional solenoid valve cannot be changed over even if the valve body moves slightly between each position.
Moreover, when the joystick is operated rapidly, the current output to the proportional solenoid valve appears suddenly after the time a from starting operation has elapsed, so the working oil flowrate controlled by the proportional solenoid valve changes suddenly, and the work device driven by the actuator suffers a shock.
It is therefore an object of this invention to provide a signal processor for a joystick input device which maintains good response when the joystick starts to be operated, and prevents a shock from occurring in an actuator or the like corresponding to sudden operation of the joystick.